Polyether Ether Ketone: A High-Performance Engineering Thermoplastic

 

Polyether Ether Ketone

Polyether ether ketone, commonly known as PEEK, is a semi-crystalline thermoplastic belonging to the polyaryletherketone (PAEK) family. PEEK polymer was first developed in the late 1970s as an alternative to metal in applications requiring high strength, rigidity and toughness at elevated temperatures. It has excellent mechanical and chemical resistance properties which make it suitable for use in demanding environments.

Physical Properties of PEEK

Polyether Ether Ketone (PEEK)  is known for its high strength, stiffness and toughness even at elevated temperatures. Some key physical properties of PEEK include:

- Density: 1.3 g/cm3, making it one of the lightest high performance polymers. This property aids in weight reduction for parts.

- Melting Point: 343°C. PEEK retains its mechanical integrity up to 260°C and can withstand short term peak temperatures up to 300°C.

- Glass Transition Temperature (Tg): Between 143°C to 150°C. Above this temperature, the polymer transitions from a brittle glassy state to a rubbery state with more impact resistance.

- Chemical Resistance: PEEK exhibits outstanding resistance to a wide range of chemicals including organic solvents, acids, bases and salt solutions. It is impervious to almost all chemicals except oxidizing acids.

- Excellent Dimensional Stability: PEEK has very low moisture absorption of only 0.1-0.2% when immersed in water. This results in negligible swelling or distortion on exposure to moisture/solvents.

Mechanical Properties of PEEK

The mechanical properties of PEEK make it a popular engineering material replacing metals in many applications:

- Tensile Strength: Excellent tensile strength of 90-100 MPa with high retained strength even at raised temperatures up to 150°C.

- Stiffness & Flexural Modulus: Comparable to Metals - Flexural modulus of 3.6 GPa provides strong but lightweight structures.

- Impact Strength: Outstanding toughness - un-notched Izod impact strength of 80-110 J/m. PEEK maintains impact resistance better than other thermoplastics even at sub-zero temperatures.

- Fatigue & Compressive Strength: Superior fatigue strength and compressive strength properties allow PEEK parts to withstand dynamic cyclic loading conditions.

- Wear Resistance: Very low coefficient of friction of 0.25 and high abrasion resistance. PEEK parts can be used in high wear applications.

Processing of PEEK

PEEK, being a semi-crystalline thermoplastic, can be processed like other plastics using various manufacturing techniques:

- Injection Molding: Most common method used to manufacture complex parts in high volumes due to PEEK's excellent flow characteristics. Cools rapidly for net shape parts.

- Machining: Can be machined easily after injection molding using conventional metalworking tools. Provides dimensional precision and intricate details.

- 3D Printing: Emerging as a useful technique for low volume production of complex PEEK parts using laser sintering or powder bed fusion methods.

- Extrusion: Used to produce profiles, tubes, pipes and sheets which are further thermoformed or welded to make finished products.

- Bonding and Joining: PEEK lends itself for adhesive bonding, welding, screwing etc. It can also be bonded with fillers to reinforce weak areas.

Applications of PEEK

Due to its unique properties, PEEK has found diverse applications replacing metals in industries such as:

- Aerospace: Engine components, fasteners, composites, structural frames operating in high load/temperature environments.

- Automotive: Distributor caps, gear parts, ignition coils and valve seats for their superior tribological properties.

- Medical: Implants, artificial joints, valves, tubes, dental brackets due to biocompatibility and sterilization capability.

- Electronics: Insulators, semiconductor mounting brackets, wire and cable insulation where heat and chemical resistance is critical.

- Industrial: Bearings, gears, pumps and valve components in ultra high performance applications.

- Consumer Goods: Sports goods (tennis rackets, bicycle parts etc.), home appliances, small industrial machines.

PEEK's excellent mechanical and chemical resistance properties along with processability and superior performance at high temperatures, have led to its wide acceptance as an advanced engineering thermoplastic replacing metals in diverse industries. PEEK components deliver long-term reliability and cost savings by reducing part counts and weight. Continued improvements in 3D printing of PEEK will further expand its applications in the future.

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